Crystal controlled circuit



July 28, 19364 I M. G, CROSBY 2,048,782

CRYSTAL CONTRLLD CIRCUIT Filed oct. 4, 1952' 2 sheets-sheet 1 /Vaouuvra/Q l flNvENToR- MURRAY 6*., CROSBY BY f3. (im

ATTORNEY- July 28, 1936.

M. G; cRosBY 2,048,782

Y CRYSTAL CONTROLLED CIRCUIT vFiled opt. 4, 1932 l r Awa/HH? v n INVENTOR- MURRAY (l- CROSBY` ATTORN EY- Patented July 28, 1936 UNITED STATES: cargar orties CRYSTAL CONTROLLED CIRCUIT Murray G. Crosby, Riverhead, Long Island, N. Y., assigner to Radio Corporation of America, a corporation of DelawareY Application October 4, i932, Serial No. 636,107V

5` Claims. (C1. 25o-36) This invention relates to improved piezo-electric crystal controlled oscillation generator circuits.

Heretofore, crystal controlled oscillation generators have been subject to frequency variation because of circuits having inductance and capacity associated therewith. Consequently, because of variations in reactance of these circuits, and also to a limited extent because of variations in tube electrode voltages, frequency drifts have occurred. To overcome such frequency changes is the principal object of my present invention and to do so, I provide a crystal controlled oscillation generator in which normally reactive circuits are replaced with a piezo-electric crystal.

Because my invention involves the use of a plurality of crystals operating at substantially the same frequency, it should be apparent that frequency drift will rarely, if ever, occur, and if it does it will be in such amounts as to be practically negligible. Consequently, my improved form of crystal controlled oscillation generator will be very suitable for a standard frequency oscillation generator.

According to my invention further, crystals Vhaving different temperature coefficients may be simultaneously used whereby the frequency of oscillation may be rendered practically independent of ambient temperature changes.

My present invention may more readily be understood both as to its mode of operation and crystals are used in the input and output circuits of a pushpull system and wherein further crystals are used for feed back purposes; and,

Figure 5 is a single tube modication of the oscillator shown in Figure 4.

Referring more specifically to Figure 1 of the drawings, a quartz piezo-electric crystal 2 is connected between the grid or cold electrode ll and Y filament 6 of a vacuum tube or electron discharge device 8. Platerpotential for plate or cold electrode l is fed `through a radio frequencyV choke l2 and a screen grid l is maintained at radio frequency ground potential by the action of a suitable by-passing condenser I6. The cold electrodes li, l 0 and M rare, of course, unequally spaced from the cathode 6 and are subjected to different unidirectional potentials. At the higher frequencies, the condenser I6 may be made of such a value as to series resonate with the inductanee of Vthe vscreen grid lead so as to positively maintain the screen grid substantially at radio frequency ground potential. Grid or control electrode bias is supplied by means of a battery I8 conductively connected to the grid ll through a radio frequency choke 2i). The crystal may be connected directly to the grid, but is preferably isolated therefrom for unidirectional potentials by means of a bypassing condenser 22 which obviously offers appreciably no impedance to high frequency or Icrystal currents. A crystal 2li is somewhat similarly connected in the anode or output circuit of ,tube 8, it being isolated from the plate potential by means of a condenser 26 and from the grid lbiasing Ypotential from the next stage by means `of another condenser l28. Both condensers 26, 428, however, offer little impedance to high frequency currents.

`It is to be noted that crystal 2li is used to replace the heretofore customary parallel tuned circuit consisting Yof an inductance coil and a variable condenserfconnected in parallel between the plate and cathode `of the oscillation generator tube 8.

The crystals 2 and 24 are ground to substantially the same desired operating frequency, care being taken that crystals 2 and 2li areground to such frequencies as to offer effectively the correct lreactance for fthe desired operating frequency.

.For example, with straight capacity feed back ffrom'th'e anode circuit to the control electrode or grid circuit, crystals 2 and 24 should be ground sofas to offer inductive reactances to the desired operating frequency. Further, crystals 2 and 24 should be'socut'from the natural crystal or so chosen as to have respectively positive and negative temperature coefficients or the reverse where- .by changes in ambient temperature will become lof a vacuum tube amplier 30 having a tunable output circuit 32. Energy from the circuit 32 may YA thencb'e Y fed linto amplifiersv and/or frequency multipliers and/or modulator 34 supplied with modulating potentials from a suitable source 36.

The resultant modulated output may then be fed to a power amplifier 38 and then radiated by means of a radiating antenna 40.

The system shown in Figure 1 may also indicate a receiving system in which case the antenna 40 would indicate a receiving antenna, 38 a radio frequency amplifier, and 34 a first detector supplied with energy from the local oscillator tube 38. Rectangle 36 would then indicate a second detector followed by suitable low frequency amplifiers and a translating device such as a syphon recorder, ear phones or loudspeaker.

In Figure 2 the crystal2 is shown connected between the control grids of tubes 8, 42 and the crystal 24 is illustrated as being connected between the plates or anodes of those tubes. The crystal 2 is isolated from the grid biasing potentials supplied to the grids through resistors 44 from source i8 by means of by-passing condensers 22, 46. Interelectrode feed back may be reduced if desired by means ofthe neutralizing condensers 48, 56 cross-connecting the anodes and control electrodes of tubes 8, 42. While the plate potential shown in Figure 2 has been shown -as being fed through radio frequency chokes I2, 54, these chokes may obviously be replaced by a resistor such as resistors 44.

The output of crystal controlled oscillator tubes 8, 42 of Figure 2, is fed through by-passing condensers 28, 56 to the pushpull connected screen grid amplifiers 30, 58 having a tunable output circuit Gil from which energy may be taken inductively as shown and fedto any suitable utilization circuit.

As described in connection with Figure 1, the crystals of Figure 2 should be ground so that the feed back voltages will be of correct phase for oscillation generation. Also, the crystals 2, 24, if desired, may be made of such material or out from the natural crystal in such a way as to have positive and negative temperature coefficients respectively, thereby preventing changes in frequency due to ambient temperature changes. Obviously, while the crystal 24 has been shown isolated from the D. C. circuits by means of bypassing condensers 62`,these condensers, if desired, may be dispensed with without affecting the radio frequency operation of the system. They are preferred, however, to safeguard the crystal against application of undesired D. C. potentials.

In the arrangement shown in Figure 1 a screen grid has been illustrated in order to reduce feed back. kThe purpose of such a reduction is, of course, to reduce the load carried by the crystal as a result of which frequency stability is enhanced. In Figure 2 the feed back control has been accomplished by means of a cross neutralized arrangement of tubes. In Figure 2 adjustment of feed back may also be accomplished by variably tapping the grids of the tubes on resistors 44. Such an arrangement utilizing a variable tap and also reduced to a single tube stage is illustrated in Figure 3.

Referring to Figure 3, neutralizing condenser 48 serves the dual function of controlling feed back as well as preventing the application of plate potential to crystal 2. As a Vfurther feed back control, the control electrode or grid is shown variably tapped to input resistor 44. If desired, in the system shown in Figure: 3, the resistor 44 may be replaced by a divided inductor and may be completely neutralized by means of kthe conto be limited in the placing of crystals ground 10 g approximately to the same frequency into circuit as shown in Figures 1 to 3 inclusive.

In the arrangement shown in Figure 5 the screen grid tube B has a screen grid so effectively grounded and its Ainput and output circuits 15 shielded so that, insufficient feed back for oscillation generation occurs. Fee-d back is then accomplished by means of crystal 62 connected between thejplate and grid of tube 8. Crystals 12 and 24 shown in Figure 5 correspond to crystals 2 and 24 of Figure 1. GridA and controlelectrode bias shownY in Figure 5 is obtained by means of grid leak resistor 64, the screen grid is grounded for radio frequency currents -by means of condensers 66 and polarized through the action of 25 voltage droppingresistor 68. Anode potential is supplied to the plate of tube 8 through resistor 'I across which crystal 24 is connected inY parallel. The crystals 2, 62 and 24 shown-in Figure5 are shown provided with electrodes which may be 30 variably spaced from the crystal, or with variable condensers connected in series therewith for 'adjustment purposes.

Crystals 12, 62 and 24 of Figure 5 are ground approximately to the same operating frequency. 35 By discreet choice of frequencies and also by correct variation of capacities in series with crystals 12, 62 and 24 the phase of the voltages fed back'will be correct for oscillation generation at a frequency which is approximately the mean of the frequencies of crystals 12, 62'and 24.Y

The pushpull arrangement of the oscillation generator shown in Figure 5 is illustrated in Figure 4. Crystals 2 and 24 form the grid circuit andplate circuit, or respectively the input' and output circuit frequency controllingcrystals. Crystals62 and'12 forrnthe sole vfeed back circuits from'the anode circuits *to-the control electrode or grid circuits. As an added adjustment and refinement, crystal 24 may not only bev provided `with, an "adjustable electrodev 14 but also may be placed serially between the two variable coupling condensers 16, 18. As in Figure 2, output energy may vbe Lfed through bypassing condensersl, 56 to the pushpull connected electron dischargedevicesf' 3, 56 whose output energy isv fed to any suitable'utilization circuit. v

It is to be clearly. understood that during operation, all of the crystals in each of the systems60 described oscillate at a common frequency which in general lies between the natural frequencies of the crystals included in circuit. That 'is' to say, the frequency at which the crystals oscillate differs slightly from their natural resonant fre- 65 quencies in any particular circuit such as described above. Y

Having thus' described my invention, what I claim is: Q

1. An oscillation generator com metically sealed container wherein are contained an electron emitting vcathode 'and a plurality of relatively cold electrodes including an anodev and a control [grid unequally spaced from said'cathv ode, 'a'piezo-electric crystal connected between'175 prising an her-3.70

said anode and said control grid, and a piezoelectric crystal connected between a cold electrode and said cathode, said crystals being mechanically isolated from each other and being ground to approximately the same frequency and to such specific frequencies that oscillations are generated by said device at a constant frequency substantially that of the common operating frequency of said crystals.

2. An oscillation generator comprising an electron discharge device having an anode a cathode and a control grid, a piezo-electric crystal connected between said control grid and anode, another piezo-electric crystal connected between said anode and cathode, said crystals being ground to substantially like frequency and being mechanically isolated from each other, and, means for reducing capacity feed back between said anode and control electrode.

3. Apparatus as claimed in the preceding claim characterized by the fact that said means for reducing interelectrode feed back is in the form of a, screen grid maintained substantially at ground potential.

4. An oscillation generator comprising a closed container wherein are contained an electron emitting cathode and a plurality of cold electrodes unequally spaced from Said cathode, a

piezo-electric crystal connected between one of said cold electrodes and said cathode, a piezoelectric crystal connected between said other cold electrode and said cathode, and a third piezo-electric crystal connected between said pair of cold electrodes, said crystals being mechanically isolated from each other and being ground to approximately the same frequency and to such specic frequencies that oscillations are generated by said device at avconstant frequency substantially that of the common operating frequency of said crystals.

5. In an oscillation generator an electron discharge tube net work having at least one electron discharge tube adapted to produce oscillations between its electrodes, means including a plurality of piezo-electric devices each connected across different pairs of said electrodes for maintaining constant the frequency of said oscillations, said piezo-electric devices being so ground as to obtain substantially the same frequency characteristics and being mechanically isolated one from another, and means for feeding back energy non-inductively from the output side to the input side of said network 25 through one of said piezo-electric devices.

MURRAY G. CROSBY. 

